US2787520A - Process for producing piezoelectric transducers - Google Patents

Process for producing piezoelectric transducers Download PDF

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Publication number
US2787520A
US2787520A US275451A US27545152A US2787520A US 2787520 A US2787520 A US 2787520A US 275451 A US275451 A US 275451A US 27545152 A US27545152 A US 27545152A US 2787520 A US2787520 A US 2787520A
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Prior art keywords
particles
binder
aggregate
solid
piezoelectric transducers
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US275451A
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Edwin P Meiners
Glenn A Schurman
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California Research LLC
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California Research LLC
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    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10NELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00Piezoelectric or electrostrictive devices
    • H10N30/80Constructional details
    • H10N30/85Piezoelectric or electrostrictive active materials
    • H10N30/853Ceramic compositions
    • H10N30/8536Alkaline earth metal based oxides, e.g. barium titanates
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10NELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00Piezoelectric or electrostrictive devices
    • H10N30/01Manufacture or treatment
    • H10N30/04Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
    • H10N30/045Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning by polarising
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10NELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00Piezoelectric or electrostrictive devices
    • H10N30/01Manufacture or treatment
    • H10N30/09Forming piezoelectric or electrostrictive materials
    • H10N30/093Forming inorganic materials
    • H10N30/097Forming inorganic materials by sintering
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00Metal working
    • Y10T29/42Piezoelectric device making

Definitions

  • This invention relates to a process for making piezoelectric transducers and to the transducers formed by the process, and particularly refers to ceramic blanks for transducers formed from solid finely-divided polycrystalline aggregates bonded together by a thermoplastic binder.
  • transducers of this kind have been formed by mixing a suitable aggregate such as barium titanate with a small amount of glass-forming oxide, such as silica, with possible additions of alumina, magnesia or calcium oxide, the whole being brought to a sufficiently high temperature, for example 1300 C., to sinter the mass into a solid body which may be subsequently ground to any desired form.
  • a suitable aggregate such as barium titanate
  • glass-forming oxide such as silica
  • alumina, magnesia or calcium oxide alumina, magnesia or calcium oxide
  • the body may be polarized by applying a unidirectional electrical potential between electrodes formed on opposed faces of said body, while holding the body at a high temperature, to produce an electrical field of at least 25,000 volts per centimeter of thickness for a time suflicient to produce a substantial amount of piezoelectric effect in the body.
  • polarized by applying a unidirectional electrical potential between electrodes formed on opposed faces of said body, while holding the body at a high temperature, to produce an electrical field of at least 25,000 volts per centimeter of thickness for a time suflicient to produce a substantial amount of piezoelectric effect in the body.
  • a disadvantage of the prior method of producing ceramic transducers of this kind was the necessity of several separate operations, first pressing the powdered aggregate to approximate shape, then heating it twice, first at high temperature to sinter the binding material and then at a lower temperature while polarizing, after which the unit was finally ground to exact dimensions. Also, it has been found that the mode of distribution of the binder for the aggregate is relatively critical both as to the homogeneity and mechanical strength of the finished unit and also as to its electrical properties. It has been found, for example, that a mixture of finely divided dry binder material with the ceramic aggregate particles will not produce as desirable a structure, presumably due to clumping of the components, during heating and forming, which adversely affects the final unit.
  • Another object is to provide an improved procedure for preparing the ceramic aggregate prior to the pressing into the final form and dimensions of the transducer unit, as well as simplification of such pressing and molding procedures.
  • a preferred aggregate of barium titanate or barium strontium titanate in finely divided form for example Patented Apr. 2, P357 350 mesh, is combined with about 5 to 10 percent by weight of binder, such as the thermoplastic methyl methacrylate polymer known as Lucite, which has previously been dissolved in an excess of solvent such as ethyl acetate in a ratio of 1 gram of solid polymer to about 10 cc. of ethyl acetate. After thorough agitation to insure adequate wetting of all of the finely divided aggregate particles, the solvent is evaporated, also with agitation, to leave each particle coated with a thin and tightly adherent layer of the solid thermoplastic binding agent.
  • binder such as the thermoplastic methyl methacrylate polymer known as Lucite
  • solvent is evaporated, also with agitation, to leave each particle coated with a thin and tightly adherent layer of the solid thermoplastic binding agent.
  • the dry coated particles are redivided, for example by being again ground to about 300 mesh, after which they can be formed into any desired and final shape by injection or other molding procedures at a relatively low temperature, such as C.
  • the unit may be polarized to develop its piezoelectric properties, for example by applying a direct current potential between metallic electrodes suitably secured or formed upon opposed faces to produce a field of about 25,000 volts per cm. thickness for a period of at least 1 hour and at room temperature, or at any suitable temperature below the softening point of the thermoplastic binder.
  • a particular advantage of the intia'lly coated ceramic aggregate particles produced and utilized by this process is their case of handling in the final molding step, as they flow readily in the moderately heated mold and can thus be injection molded to exceedingly close dimensional tolerances and in large sizes at moderate forces.
  • a further advantage of the final transducer element or unit formed by this process is its superior resistance to moisture, its smooth and glassy outer surface, and particularly its desirable internal damping characteristics.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Ceramic Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Description

United rates Patent PROCESS FOR PRODUQING PIEZIBELECERHZ TRANSDUCERS Edwin P. Meiners and Glenn A. Schurman, Whittier, Califl, assignors to California Research Corporation, San Francisco, Calif, a corporation of Delaware No Drawing. Application March 7, 1952, Serial No. 275,451
3 Claims. (Cl. 2925.35)
This invention relates to a process for making piezoelectric transducers and to the transducers formed by the process, and particularly refers to ceramic blanks for transducers formed from solid finely-divided polycrystalline aggregates bonded together by a thermoplastic binder.
Heretofore transducers of this kind have been formed by mixing a suitable aggregate such as barium titanate with a small amount of glass-forming oxide, such as silica, with possible additions of alumina, magnesia or calcium oxide, the whole being brought to a sufficiently high temperature, for example 1300 C., to sinter the mass into a solid body which may be subsequently ground to any desired form. In certain cases thermosetting resins such as phenolformaldehyde have been proposed for a bonding agent. After sintering, the body may be polarized by applying a unidirectional electrical potential between electrodes formed on opposed faces of said body, while holding the body at a high temperature, to produce an electrical field of at least 25,000 volts per centimeter of thickness for a time suflicient to produce a substantial amount of piezoelectric effect in the body. Such procedures are described in U. S. Patent 2,538,554, issued January 16, 1951, to W. L. Cherry.
A disadvantage of the prior method of producing ceramic transducers of this kind was the necessity of several separate operations, first pressing the powdered aggregate to approximate shape, then heating it twice, first at high temperature to sinter the binding material and then at a lower temperature while polarizing, after which the unit was finally ground to exact dimensions. Also, it has been found that the mode of distribution of the binder for the aggregate is relatively critical both as to the homogeneity and mechanical strength of the finished unit and also as to its electrical properties. It has been found, for example, that a mixture of finely divided dry binder material with the ceramic aggregate particles will not produce as desirable a structure, presumably due to clumping of the components, during heating and forming, which adversely affects the final unit.
It is an object of this invention to provide an improved procedure for producing a piezoelectric transducer that involves fewer operations and results in a product having desirable properties as compared to those heretofore availab e.
Another object is to provide an improved procedure for preparing the ceramic aggregate prior to the pressing into the final form and dimensions of the transducer unit, as well as simplification of such pressing and molding procedures.
These and other objects and advantages of this invention will be further apparent from the following description of a preferred procedure for preparing ceramic transducer units.
A preferred aggregate of barium titanate or barium strontium titanate in finely divided form, for example Patented Apr. 2, P357 350 mesh, is combined with about 5 to 10 percent by weight of binder, such as the thermoplastic methyl methacrylate polymer known as Lucite, which has previously been dissolved in an excess of solvent such as ethyl acetate in a ratio of 1 gram of solid polymer to about 10 cc. of ethyl acetate. After thorough agitation to insure adequate wetting of all of the finely divided aggregate particles, the solvent is evaporated, also with agitation, to leave each particle coated with a thin and tightly adherent layer of the solid thermoplastic binding agent. The dry coated particles are redivided, for example by being again ground to about 300 mesh, after which they can be formed into any desired and final shape by injection or other molding procedures at a relatively low temperature, such as C. After such forming is complete, the unit may be polarized to develop its piezoelectric properties, for example by applying a direct current potential between metallic electrodes suitably secured or formed upon opposed faces to produce a field of about 25,000 volts per cm. thickness for a period of at least 1 hour and at room temperature, or at any suitable temperature below the softening point of the thermoplastic binder.
A particular advantage of the intia'lly coated ceramic aggregate particles produced and utilized by this process is their case of handling in the final molding step, as they flow readily in the moderately heated mold and can thus be injection molded to exceedingly close dimensional tolerances and in large sizes at moderate forces.
A further advantage of the final transducer element or unit formed by this process is its superior resistance to moisture, its smooth and glassy outer surface, and particularly its desirable internal damping characteristics.
Although only a single example has been given of the process and the product resulting therefrom, it is apparent that changes, both in the aggregate material and in the dielectric thermoplastic binder, as Well as in the proportions of each, could be made without departing from the invention, which appears to reside in the precoating of the finely divided aggregate particles with the binder in solid form, followed by redivision and final molding to finished dimensions. Accordingly, all such changes that come within the scope of the appended claims are intended to be embraced thereby.
We claim:
1. In the manufacture of piezoelectric transducer units from a solid polycrystalline aggregate of mineral crystals and a thermoplastic binder, the steps of coating particles of said aggregate with a solution of said binder, evaporating the solvent from said particles to leave a solid coating of binder on said particles, redividing said coated particles, and molding said particles to the final form of said transducer unit.
2. In the material according to claim 1, the added step of electrically polarizing the final form of said transducer unit at a temperature below the softening temperature of said binder.
3. In the method according to claim 1, the added steps of securing electrodes to opposite faces of said transducer and applying a polarizing potential between said electrodes to produce a permanent piezoelectric effect in said unit.
References Cited in the file of this patent UNITED STATES PATENTS 1,886,234 Meissner Nov. 1, 1932 2,420,652 Chilowski May 13, 1947 2,420,864 Chilowsky May 20, 1947 2,540,412 Adler Feb. 6, 1951 FOREIGN PATENTS 584,672 Great Britain Jan. 21, 1941

Claims (1)

1. IN THE MANUFACTURE OF PIEZOELECTRIC TRANSDUCER UNITS FROM A SOLID POLYCRYSTALLINE AGGREGATE OF MINERAL CRYSTALS AND A THERMOPLASTIC BINDER, THE STEPS OF COATING PARTICLES OF SAID AGGREGATE WITH A SOLUTION OF SAID BINDER, EVAPORATING THE SOLVENT FROM SAID PARTICLES TO LEAVE A SOLID COATING OF BINDER ON SAID PARTICLES, REDIVIDING SAID COATED PARTICLES, AND MOLDING SAID PARTICLES TO THE FINAL FORM OF SAID TRANSDUCER UNIT.
US275451A 1952-03-07 1952-03-07 Process for producing piezoelectric transducers Expired - Lifetime US2787520A (en)

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2892107A (en) * 1953-12-21 1959-06-23 Clevite Corp Cellular ceramic electromechanical transducers
US3042550A (en) * 1958-05-23 1962-07-03 Corning Glass Works Solid delay line improvements
US3054004A (en) * 1957-06-24 1962-09-11 Vitro Corp Of America Piezoelectric crystal holder
US3150275A (en) * 1959-07-17 1964-09-22 Corning Glass Works Sectional transducer
US3202962A (en) * 1959-09-03 1965-08-24 Honeywell Inc Transducer
DE1466189B1 (en) * 1964-08-10 1970-06-25 Nippon Electric Co Method for the piezoelectric activation of a ferroelectric substance
US4572981A (en) * 1983-08-15 1986-02-25 North American Philips Corporation Transducer comprising composite electrical materials

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1886234A (en) * 1927-12-21 1932-11-01 Telefunken Gmbh Method of making high grade dielectric materials
GB584672A (en) * 1944-01-14 1947-01-21 Erich Schaefer Improvements in or relating to electrical condensers having plastic film dielectrics
US2420652A (en) * 1944-04-08 1947-05-20 Chilowsky Constantin Method and apparatus for making artificial piezoelectric elements
US2420864A (en) * 1943-04-17 1947-05-20 Chilowsky Constantin Piezoelectric plastic material and method of making same
US2540412A (en) * 1947-12-26 1951-02-06 Zenith Radio Corp Piezoelectric transducer and method for producing same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1886234A (en) * 1927-12-21 1932-11-01 Telefunken Gmbh Method of making high grade dielectric materials
US2420864A (en) * 1943-04-17 1947-05-20 Chilowsky Constantin Piezoelectric plastic material and method of making same
GB584672A (en) * 1944-01-14 1947-01-21 Erich Schaefer Improvements in or relating to electrical condensers having plastic film dielectrics
US2420652A (en) * 1944-04-08 1947-05-20 Chilowsky Constantin Method and apparatus for making artificial piezoelectric elements
US2540412A (en) * 1947-12-26 1951-02-06 Zenith Radio Corp Piezoelectric transducer and method for producing same

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2892107A (en) * 1953-12-21 1959-06-23 Clevite Corp Cellular ceramic electromechanical transducers
US3054004A (en) * 1957-06-24 1962-09-11 Vitro Corp Of America Piezoelectric crystal holder
US3042550A (en) * 1958-05-23 1962-07-03 Corning Glass Works Solid delay line improvements
US3150275A (en) * 1959-07-17 1964-09-22 Corning Glass Works Sectional transducer
US3202962A (en) * 1959-09-03 1965-08-24 Honeywell Inc Transducer
DE1466189B1 (en) * 1964-08-10 1970-06-25 Nippon Electric Co Method for the piezoelectric activation of a ferroelectric substance
US4572981A (en) * 1983-08-15 1986-02-25 North American Philips Corporation Transducer comprising composite electrical materials

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